These four swans are really hooting it up. The quartet began when two pairs encouraged their mates with lean-forward and wing-quiver calls. But the quivering wing display is also used in antagonistic encounters. When the males got too close the dominant male had had enough. He rushed the other one.
Whoa! The less aggressive male immediately sat on the water in a submissive posture and the situation defused. Watch him curl his neck down in an S position and look away.
Tundra swans can make music together. Sometimes they jazz it up.
We’ve all heard the story that storks bring babies. It was Grandma’s easy to answer to “Where do babies come from?”
The legend began where white storks nest in northern Europe, often in close proximity to humans. Their care for their young made them symbols of parental devotion. Slavic folklore held that storks brought unborn souls from paradise to earth in the spring and summer. That’s when the storks returned to northern Europe from their long migration to Africa.
But in the past 30 years many of them have stopped migrating. Large numbers are hanging out in Spain and Portugal. In 1995 there were 1,108 winter storks in Portugal. By 2008 there were 10,000. The number keeps growing and some of them never leave. Many stay year-round to raise their families.
The obvious attraction is Portugal’s landfills. Though white storks are carnivores, they love hanging out at the dump for an easy meal. Do the landfill storks merely visit for the winter? Do they move to other places in Portugal for the breeding season? And where would that be?
Researchers from the University of East Anglia have begun a one year study of stork migration. They’ve captured and tagged 15 adult white storks with satellite monitors to transmit each stork’s location and activity five times per day. The tags are smart enough to record whether the stork’s head is down in a feeding position.
The study is coming at a good time for the birds. In the 20th century white storks declined so badly that they had to be reintroduced in some countries. Now they’ve made a comeback at the dumps but Portugal is slowly replacing its open landfills with covered facilities to process waste food. Where will the storks go?
The study is important for Grandma, too. If the storks don’t leave Portugal, they won’t be bringing babies to Northern Europe anymore. Uh oh!
After a week near western gulls in San Diego I got pretty used to seeing individual gulls perched high, watching the others fly by. Inevitably, the lone gull would throw his head back and give the long call when other gulls flew over. What did he mean?
The “long call” is used in many contexts, as a greeting between mates or a statement about territory. In this video two great black-backed gulls give the long call when they fight over a fish. Watch the video and I’ll tell you what I think about their interactions.
Their gestures tell the tale.
The hungry gull (HG) approaches, bowed low in a threatening gesture.
The eating gull (EG) sees the threat and opens his wings, “Back off!”
HG turns away and gives the Long Call: He hunches over, bows his head, then lifts it high leaning his body at an oblique angle and calling loudly. You might think he’s not talking to EG because he’s not looking at him. Far from it! By turning away he’s avoiding direct confrontation. Perhaps he’s trying appeasement.
That didn’t work. HG walks past EG without looking at him directly. As he approaches EG’s tail he gets an idea.
Tail pulling didn’t work at all, so the hungry gull bows low (a threat) and walks to the front of EG. Facing him and opening his wings (again, a threat), he tries to steal the fish.
Finally the eating gull has had enough. The two fight. EG quickly wins. Hungry Gull retreats while EG gives the long call in triumph, and then resumes his meal.
What’s the relative stature of these gulls? My guess is that EG (the eating gull) outranks HG (hungry gull), but HG is willing to test the limits.
In Africa sunbirds fill the ecological niche that hummingbirds fill here. Like hummingbirds, they feed on nectar, have long down-curved bills and come in beautiful iridescent colors. The main difference is that sunbirds perch instead of hover.
Like hummingbirds, sunbirds also pugnaciously defend their nectar sources and spend a lot of time chasing and fighting. What is the advantage in doing this? Doesn’t it cost more energy than peaceable feeding?
In 1975 Gill and Wolf studied the energy expended by territorial golden-winged sunbirds in Kenya. Their results were a bit surprising. It costs less energy per day to defend really good nectar sources than it does to feed at undefended low-nectar flowers.
Here’s the math:
Undefended flowers have less nectar because so many birds are feeding at them. Foraging burns 4 kilojoules of energy per hour but it takes 8 hours to get enough food. 8 hours * 4 kilojoules/hour = 32 kilojoules burned.
Defended flowers have twice as much nectar so it takes only 4 hours to get the same energy. 4 hours * 4 kilojoules/hour = 16 kilojoules burned while foraging.
Defending these flowers is energy intensive (12.5 kilojoules/hour) but if it doesn’t take much time it’s worth it. If it only takes 20 minutes to defend those flowers in that same 8 hour period the results are: 0.33 hour * 12.5 kilojoules/hour = 3.7 kilojoules burned in defense.
What does a territorial sunbird do with all that extra time? He sits around and watches his flowers. 3.7 hours * 1.7 kilojoules/hour = 6.3 kilojoules spent sitting.
Therefore his total energy expenditure is 26 kilojoules, a savings of 6 kilojoules in 8 hours.
That’s why hummingbirds are so belligerent at our feeders. They’re making the calculation that defending a great food source is the cheapest way to go.
Photo of a golden-winged sunbird from Wikimedia Commons. Click on the image to see the original.
Today’s Tenth Page is inspired by page 310 of Ornithology by Frank B. Gill.)
If you haven’t been watching PixController’s eastern screech-owl webcams you’ll want to start now.
Back in October when I first wrote about the webcams, eastern screech-owls were just starting their winter-roost season. The birds hadn’t chosen preferred boxes and a squirrel was time-sharing in one of them.
Since then two owls have sorted out who roosts where. They’re definitely aware of each other because they sometimes visit each others’ roosts or eat each others’ cached food.
This week they’ve been busy in Owl Boxes #2, #6 and #7. On Tuesday night the owl nicknamed “Allie” caught and cached a mourning dove in Owl Box #2. Last night she came back to eat it. The motion detection cameras keep track of the owls so you don’t have to stay up all night. Click here to see recent archives of owl activity.
Now that Winter is ending, things are about to get very interesting. Eastern screech-owls nest in March. Will they nest in one of the boxes?
Click here or on the image above to watch PixController’s Eastern Screech-owl Live Webcams. You can also follow PixController on Facebook where Bill Powers posts the day’s best photos from his many webcam installations.
If you have to sit outdoors in winter, you’re bound to get snowed on.
Last month during a particularly wet snowfall, Gregg Diskin found this red-tailed hawk perched in Schenley Park. The bird was trying to stay warm and dry but it was a challenge. His feathers were wet and his feet were getting cold.
See how he’s tucked one foot into his breast feathers? It looks like he’s holding his coat closed. Brrrrr!
Fortunately feathers are very good insulation. You don’t realize how well they work until the hawk scratches his head.
We’re not the only ones who celebrate love this month. February is raptor courtship time.
Last year on Valentine’s Day the Decorah Eagles nestcam captured the bald eagles, “Mom and Dad”, vocalizing and mating.
This year the eagles have built a second nest that’s closer to the fish hatchery and not on camera! At this point it’s unclear which nest the eagles will use, but they’ll certainly disappoint their 60,500 followers if they choose the off camera site.
Pittsburgh’s “falconuts” experienced that disappointment a year ago when Dori and Louie chose a new nest site Downtown. Unfortunately it looks like the peregrines aren’t coming home to the Gulf Tower so we’re going to have another year of off-camera love birds.
How do you survey a population of owls who are afraid to make noise? Dogs to the rescue!
In 1990 northern spotted owls were listed as Threatened under the Endangered Species Act. Since then their population has been surveyed year after year, but despite changes in logging practices northern spotted owls continue to decline 3.7% per year.
Part of the problem could be that some owls have fallen silent and are impossible to count. The typical survey method is to play an owl recording and listen for the owl to respond. But barred owls have infiltrated the old growth forest, displaced northern spotted owls, and sometimes killed them. Some northern spotted owls would rather not respond when the tapes are played. They don’t want to give themselves away.
So how do you count these owls?
Researchers at the University of Washington trained two dogs, Max and Shrek, to identify owl pellets by species! Amazingly, the dogs can smell the difference in regurgitated mouse bones from a barred owl versus a northern spotted owl.
The team takes the dogs out for a spin in the forest. They don’t use recordings at all. The dogs sniff for pellets below owl roosts and are so good at identifying the species that they have a 30% better success rate at finding northern spotted owls than the recordings do.
Here’s Max triumphant. See the northern spotted owl in the tree above him?